Electro-Hydrodynamics and Kinetic Modeling of Dry and Humid Air Flows Activated by Corona Discharges

The present work is devoted to the 2D simulation of a point-to-plane Atmospheric Corona Discharge Reactor (ACDR) powered by a DC high voltage supply.The corona reactor is periodically crossed by thin mono filamentary streamers with a natural repetition frequency of some tens of kHz.The study compares the results obtained in dry air and in air mixed with a small amount of water vapour (humid air).The simulation involves the electro-dynamics,chemical kinetics and neutral gas hydrodynamics phenomena that influence the kinetics of the chemical species transformation.Each discharge lasts about one hundred of a nanosecond while the post-discharge occurring between two successive discharges lasts one hundred of a microsecond.The ACDR is crossed by a lateral dry or humid air flow initially polluted with 400 ppm of NO.After 5 ms,the time corresponding to the occurrence of 50 successive discharge/post-discharge phases,a higher NO removal rate and a lower ozone production rate are found in humid air.This change is due to the presence of the HO2 species formed from the H primary radical in the discharge zone.     

Treatment of Dyeing Wastewater by Using Positive Pulsed Corona Discharge to Water Surface

This study investigated the treatment of textile-dyeing wastewater by using an electrical discharge technique （positive pulsed corona discharge）. The high-voltage electrode was placed above the surface Of the wastewater while the ground electrode was submerged in the wastewater. The electrical discharge starting at the tip of the high voltage electrode propagated toward the surface of the wastewater, producing various oxidative radicals and ozone. Oxygen was used as the working gas instead of air to prevent nitrogen oxides from forming. The simulated wastewater was made up with amaranth, which is a kind of azo dye. The results obtained showed that the chromaticity of the wastewater was almost completely removed within an hour. The ultraviolet/visible spectra of the wastewater treated by the electrical discharge revealed that the total hydrocarbon level also decreased significantly.     

An Alternative Empirical Formula for Positive Corona Discharge I-V Characteristics in Point-to-Plate Electrode Geometry

Experimental data are presented for a study on the dependence of the I-V character- istics of the corona discharge on pressure and electrode spacing using point-to-plane electrode con- figuration. These experimental data are obtained by a fast, automatic computer data-acquisition system. The data are used to suggest an alternative dimensionally self-consistent empirical equa- tion for the parameterization of the I-V curves. The formula eliminates the need for any prior assumptions concerning the inception voltage, as is customary in this type of work.     

An Alternative Empirical Formula for Positive Corona Discharge Ⅰ-ⅤCharacteristics in Point-to-Plate Electrode Geometry

Experimental data are presented for a study on the dependence of the I-V characteristics of the corona discharge on pressure and electrode spacing using point-to-plane electrode configuration.These experimental data are obtained by a fast,automatic computer data-acquisition system.The data are used to suggest an alternative dimensionally self-consistent empirical equation for the parameterization of the I-V curves.The formula eliminates the need for any prior assumptions concerning the inception voltage,as is customary in this type of work.     

The Experimental Investigations of Dielectric Barrier Discharge and Pulse Corona Discharge in Air Cleaning

The dielectric barrier discharge (DBD) and pulse corona discharge(POD) plasmagenerator was used to remove NHa, H2S, C7H8 etc. from atmosphere. The principle and charac-teristic of the two ways was discussed in the article. The test shows the result of PCD is betterthan that of DBD.     

Removal of NO and SO2 in Corona Discharge Plasma Reactor with Water Film

In this paper, a novel type of a corona discharge plasma reactor was designed, which consists of needle-plate-combined electrodes, in which a series of needle electrodes are placed in a glass container filled with flue gas, and a plate electrode is immersed in the water. Based on this model, the removal of NO and SO2 was tested experimentally. In addition, the effect of streamer polarity on the reduction of SO2 and NO was investigated in detail. The experimental results show that the corona wind formed between the high-voltage needle electrode and the water by corona discharge enhances the cleaning efficiency of the flue gas because of the presence of water, and the cleaning efficiency will increase with the increase of applied dc voltage within a definite range. The removal efficiency of SO2 up to 98%, and about 85% of NO~ removal under suitable conditions is obtained in our experiments.     

Electrical Characteristics of Pulsed Corona Discharge Plasmas in Chitosan Solution

Pulsed discharge plasma has exhibited active potential to prepare low molecular weight chitosan. In the present study, the viscosity of ehitosan solution was decreased noticeably after treated with pulsed corona discharge plasma. An experimental investigation on electrical characteristics of pulsed corona discharge plasma in chitosan solution was conducted with a view toward getting insight into discharge process. Factors affecting I-V curve, single pulse injec- tion energy and pulse width were studied. Experimental results showed positive effect of pulsed peak voltage on discharge plasma in chitosan solution. Pulse-forming capacitor greatly influenced the discharge form, and 4 nF was observed as a suitable value for efficiently generating stable discharge plasmas. As the electrode distance was larger than 10 ram, it had slight impact on dis- charge plasma due to the excellent conductive-property of chitosan solution. The injection energy significantly increased with air flow rate, while the pulse width hardly changed as the air flow rate increased from 0.5 m^3/h to 1.0 m^3/h. This study is expected to provide reference for promoting the application of pulsed corona discharge plasma to ehitosan solution treatment.     

Branch Structure of Corona Discharge： Experimental Simulation and Chemical Properties

The branch structure of corona discharge has been investigated via C2H2 corona discharge. Carbon filament with excellent branch structure is formed in the discharge. This carbon filament offers a direct mimic of the branch structure of corona discharge. It provides a very useful way to study on the average energy, physical and chemical characteristics of corona discharge. On this basis, the chemical property of corona discharge for methane conversion is discussed.     

Numerical Modelling Point-to-Plane of Negative Corona Discharge in N_2 Under Non-Uniform Electric Field

The paper presents a simulation model of the negative corona discharge in N_2 under various pressures.The simulated discharge is of a negative point-to-plane mass type,with an inter-electrode separation distance of 20 mm and a symmetry about the axis of discharge.This simulation investigates the behavior of the neutral density and temperature for different pressures in the range of 0.1-10.0 bar.The spatial and temporal evolution of the neutral gas is analyzed based upon the equations of continuity,momentum and energy in a two-dimensional cylindrical geometry model.For that geometry of the system,the FCT(Flux Corrected Transport) technique was adopted.The results show that the pressure plays a significant role of the neutrals dynamics.     

Removal of Volatile Organic Compounds (VOCs) Mixture by Multi-Pin-Mesh Corona Discharge Combined with Pulsed High-Voltage

Removal of single component and binary mixtures of benzene and m-xylene using a multi-pin-mesh reactor was studied to find the decomposition characteristics, carbon balance and CO2 selectivity. The decomposition rate of benzene in mixture was approximately 16% lower than that of single component benzene. However, the decomposition rate of m-xylene in mixture was slightly higher than that of single component m-xylene. Carbon balance of the mixture decomposition process achieved a lower level than that of single component benzene/m-xylene. Increase in the specific input energy was helpful to improve CO2 selectivity in the single component decomposition process, while the specific input energy had a negligible effect on CO2 selectivity in the mixture decomposition process. By changing the oxygen content in background gas, we found that different types of radicals showed different reaction activities toward benzene and m-xylene. Benzene was more likely to react with nitrogen-containing radicals, while m-xylene was more likely to react with oxygen-containing radicals.     

The Study of Active Atoms in High-Voltage Pulsed Coronal Discharge by Optical Diagnostics

In this study, the emission spectra of active atoms O (3p^5p → 3s^5S^02 777.4 nm),Ha (3P→2S 656.3 nm) and N (3p^4P→ 3s^4S^0 742.3 nm, 744.2 nm, 746.8 nm) produced by thepositive high-voltage pulsed corona discharge (HVPCD) of N2 and H2O mixture in a needle-plate reactor have successfully been recorded against a severe electromagnetic interference coming from the HVPCD at one atmosphere. The effects of the peak voltage, the repetition rate of pulsed discharge and the flow rate of oxygen on the production of those active atoms are investigated. It is found that when the peak voltage and the repetition rate of the pulsed discharge are increased,the emission intensities of those active atoms rise correspondingly. And the emission intensities of O (3p^5P→3s^5S^0 777.4 nm), Hα (3P→2S 656.3 nm) and N (3p^4P→3s^4S^0 742.3 nm, 744.2 nm,746.8 nm) increase with the flow rate of oxygen (from 0 to 25 ml/min) and achieve a maximum value at a flow rate of 25 ml/min. When the flow rate of oxygen is increased further, the emission intensities of those atoms visibly decrease correspondingly. The main physicochemical processes of interaction involved between electrons, neutrals and ions are also discussed.     

Measurement of Temporally and Spatially Resolved Electron Density in the Filament of a Pulsed Spark Discharge in Water

The temporally and spatially resolved optical emission spectrum of Hα of a pulsed spark discharge in water was experimentally measured. The temporally and spatially resolved electron densities, along the radial direction of the spark filament, for a pulsed spark discharge in water with a conductivity of 100 μS/cm were investigated. The electron density in the spark filament was found to be in the 10~(18)/cm~3 order of magnitude. The highest electron density was measured at the primary stage of the spark filament, and it decreased with time. The radial distribution of electron density increased from the center to the edge of the spark filament.     

Factors Influencing the Electron Yield of Needle-Ring Pulsed Corona Discharge Electron Source for Negative Ion Mobility Spectrometer

A simple negative ion mobility spectrometer （IMS） is designed and used to investi- gate the factors that influence the number and efficiency of electrons generated by the needle-ring pulsed corona discharge electron source. Simulation with Ansoft Maxwell 12 is carried out to analyze the electric field distribution within the IMS, and to offer the basis and foundation for analyzing the measurement results. The measurement results of the quantities of electrons show that when the drift electric field strength and the ring inner diameter rise, both the number of ef- fective electrons and the effective electron rate are increased. When the discharge voltage becomes stronger, the number of effective electrons goes up while the effective electron rate goes down. In light of the simulation results, mechanisms underlying the effects of drift electric field strength, ring inner diameter, and discharge voltage on the effective electron number and effective electron rate are discussed. These will make great sense for designing negative ion mode IMS using the needle-ring pulsed corona discharge as the electron source.     

Generation of Preformed Plasma Channel for GeV-Scaled Electron Accelerator by Ablative Capillary Discharges

Generation of plasma channels by low jitter ablative capillary discharges is investi- gated experimentally in details. A time-resolved evolution and radial distributions of the electron density are measured, and proof-of-principle optical guiding experiment is conducted. A proper time window for optical guiding of a femtosecond laser pulse is found. The generated low density, long plasma channel is believed to be useful in the applications as GeV-class channel-guided laser wake¯eld accelerators and compact X-ray femetosecond coherent radiation sources.     

The detailed characteristics of positive corona current pulses in the line-to-plane electrodes

The corona current pulses generated by corona discharge are the sources of the radio interference from transmission lines and the detailed characteristics of the corona current pulses from conductor should be investigated in order to reveal their generation mechanism. In this paper, the line-to-plane electrodes are designed to measure and analyze the characteristics of corona current pulses from positive corona discharges. The influences of inter-electrode gap and line diameters on the detail characteristics of corona current pulses, such as pulse amplitude, rise time, duration time and repetition frequency, are carefully analyzed. The obtained results show that the pulse amplitude and the repetition frequency increase with the diameter of line electrode when the electric fields on the surface of line electrodes are same. With the increase of inter-electrode gap,the pulse amplitude and the repetition frequency first decrease and then turn to be stable, while the rise time first increases and finally turns to be stable. The distributions of electric field and space charges under the line electrodes are calculated, and the influences of inter-electrode gap and line electrode diameter on the experimental results are qualitatively explained.     

Generation of reactive atomic species of positive pulsed corona discharges in wetted atmospheric flows of nitrogen and oxygen

The emission spectra of excited radicals(OH(A~2E),O(3p~3 P),H_α(3P)) and emissive species(N_2~+(B~2∑_u~+),N_2(C_3Π_u)) produced by positive pulsed high-voltage needle-plane corona discharges in atmospheric N_2 and O_2 flows wetted with 10%H_2O at 80 ℃ are used to investigate the relative concentrations of the produced radicals.The results indicate that the tendencies of the concentrations of radicals with discharge conditions are similar to each other due to their similar excitation processes by electron collision.The influence of oxygen flow mixed with the nitrogen flow on the emission intensities of O(3p~5P → 3s~5S_2~.),H_α(3P → 2S),N_2_+(B~2∑_u~+ → X~2∑_g+0-0),and N_2(C~3Π_u → B~3Π_g 1-0) is presented.When the flow rate of oxygen addition is varied from 0-30 ml min~(-1),the emission intensities of O(3p~5P → 3s~5S_2~0.),H_α(3P → 2s),and N_2~+(B~2∑_u~+ →X~2∑_g 0-0) increase and reach a maximum.Then,if the oxygen flow rate increases further,the emission intensities tend to decrease.However,the intensity of N_2(C~3Π_u → B~3Π_g1-0) decreases monotonously with the increasing oxygen flow,which indicates that the electron density decreases with the increasing oxygen flow.By the tendencies of the relative intensities to N_2(C~3Π_u → B~3Π_g 1-0),the concentrations of the total produced O,H,and N_2~+ are shown to increase with the oxygen flow.Based on the reactions for the production of H and O without and with the addition of O_2,the analytic solutions for H and O production are derived in accordance with the experimental results.     

Simulation of Needle-Type Corona Electrodes by the Finite Element Method

This paper describes a software tool, called LEVSOFT, suitable for the electric field simulations of corona electrodes by the Finite Element Method （FEM）. Special attention was paid to the user friendly construction of geometries with corners and sharp points, and to the fast generation of highly refined triangular meshes and field maps. The execution of selfadaptive meshes was also implemented. These customized features make the code attractive for the simulation of needle-type corona electrodes. Some case examples involving needle type electrodes are presented.     

The Diagnosis of Plasma Parameters in Surface Alloying Technique by Optical Emission Spectrometry

Electron density （Ne） in a glow discharge plasma for the surface alloying technique is diagnosed by optical emission spectrometry （OES）. With CH4 as the feeding gas, Ne is obtained by comparing the Hβ spectrum according to the Stark broadening effect. It is noticed that Ne varies with the working pressures （30 Pa to 70 Pa） and cathode voltages （500 V to 1000 V）, respectively. Due to an abnormal glow discharge, Ne is between 1. 71 × 10^15 /cm^3 to 6.64 × 10^15 /cm^3 and increases rapidly with working gas pressures and cathode voltages. The results show that OES is a useful method to measure the plasma parameters in a surface alloying glow discharge plasma.     

Characterization of Nitrogen Glow Discharge Plasma via Optical Emission Spectrum Simulation

Optical emission spectroscopy in nitrogen glow discharge plasma is simulated, and the collision excitations and characteristic emissions of the species （N2, N2^＋, N^＋, N） are investigated by a Monte Carlo model for nitrogen molecular gas discharge. The excitation rates of the main excited states are calculated and the corresponding relation and relative magnitude between the distribution of excitation rate of a certain excited state and the distributions of the emission rates of various lines originating from this excited level are also explored. The simulated results are compared with the experimental measurements in two typical discharge conditions. The luminescence mechanism of the line N2^＋： 391.4 nm is explained based on the microscopic plasma processes. The cathode glow in N2 discharge is found to be mainly caused by N^＋ impact excitation and the intensity of cathode glow decreases with the voltage. The corresponding relation between the emission rate or intensity of the 391.4 nm line and the production rate and the density of N2^＋ is also examined.     

Decontamination of 2-Chloroethyl Ethyl Sulfide by Pulsed Corona Plasma

Decontamination of 2-chloroethyl ethyl sulfide （2-CEES, CH_3CH_2SCH_2CH_2C1） by pulsed corona plasma was investigated. The results show that 212.6 mg/m^3 of 2-CEES, with the gas flow rate of 2 m^3/h, can be decontaminated to 0.09 mg/m^3. According to the variation of the inlet and outlet concentration of 2-CEES vapor with retention time, it is found that the reaction of 2-CEES in a pulsed corona plasma system follows the first order reaction, with the reaction rate constant of 0.463 s^-1. The decontamination mechanism is discussed based on an analysis of the dissociation energy of chemical bonds and decontamination products. The C-S bond adjacent to the C1 atom will be destroyed firstly to form CH3CH2S. and .CH2CH2C1 radicals. CH3CH2S. can be decomposed to .C_2H_5 and .S..S can be oxidized to SO_2, while .C_2H_5 can be finally oxidized to CO_2 and H_2O. The C-Cl bond in the .CH_2CH_2C1 radical can be destroyed to form .CH_2CH_2. and .C1, which can be mineralized to CO_2, H_2O and HCl. The H atom in the .CH_2CH_2C1 radical can also be substituted by -C1 to form CHCl_2-CHCl_2.